In order to reduce CO2 emissions and thus limit global warming we need to reduce energy consumption. One way to do this is to make the machines that we use in everyday life, ranging from car engines to washing machine motors and bearings, more efficient. This is particularly important since there is a huge rate of growth in the use of machines in countries such as China and India as these become more prosperous. There are several strategies for increasing machine efficiency but one of the most effective is to reduce mechanical friction. So far this has been done mainly by using lower viscosity lubricants, which have less friction drag. However, this approach is reaching the end of its usefulness since, it also leads to thinner fluid films between rubbing surfaces, which eventually results in high wear as well as even more friction. The solution now lies in improving the performance of surfaces films, which can protect components and reduce friction regardless of lubricant viscosity. These are called boundary films, and must be made to form more quickly and durably, and give lower friction. This is currently impossible since, despite a century of research and widespread commercial use, there is inadequate understanding of the mechanisms by which they form.

The biggest gap in our understanding concerns the way that the rubbing process stimulates film formation. When solids are rubbed together actual contact occurs only at a few high spots on the surfaces. The conditions at these contact points are extremely severe, with very high local stresses which plastically deform the rubbing surfaces. Under such conditions, a phenomenon called "triboemission" occurs; i.e. fundamental particles such as electrons, ions and photons are ejected from the surfaces. These energetic particles promote a series of chemical reactions in the lubricant present that leads, ultimately, to the formation of protective boundary lubricating films. These particles can also have harmful effects such as causing lubricant film degradation on computer hard drives.

In order to improve boundary film formation we need to understand triboemission and its effect on lubricants. Unfortunately these processes occur between a pair of rubbing surfaces, where it is difficult to see and measure. Furthermore, particles emitted react almost instantly with the lubricant present, and are obscured by the competing influences of frictional heating and extreme pressure. This makes research on triboemission very challenging to carry out, which is why we currently know so little about it.

The research group which I aim to build will develop and apply a series of novel experimental techniques to study triboemission and to monitor its impact on lubricants and boundary film formation. The key is to look at each stage of the emission and film formation process and link these together. Particle detection apparatus will be built and incorporated into friction testing equipment. Thermal mapping will be used to distinguish triboemission from other causal factors, while fluorescence imaging (currently used mainly in biomedical applications to study molecule mobility) will help track transient reaction species in the lubricant. Additionally, the application of scanning probes will pioneer the mapping of emission and allow correlation with surface properties. In this way, the series of interactions that occur between lubricant and environment will be unravelled. With industrial support, this understanding will be used to design enhanced surface and lubricant combinations. The result will be improved friction performance and, in certain critical applications, protection of the lubricant from degradation.

This summary has focussed on engineering contacts but triboemission is also believed to play a decisive role in the lubrication of bio-contacts and micro-contacts, where friction is a significant factor in performance. These applications will also be studied in my research.

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